1. Boolean Logic

2. Basic Logic Statement Evaluates To (True or False) True False False
The sky is blue
The sky is NOT blue
The grass is pink
The grass is NOT pink
A snail is fast
A snail is NOT fast
The School is 3 stories high
The School is NOT 3 stories high
A soccer ball is round and pink
A soccer ball is NOT round and NOT pink
True
False
False
True
False
True
True
False
False
False
What do you notice when you compare the two columns?

3. Boolean Variables A Boolean variable can store only two values:
True
False
Boolean variable naming is the same as all other variable naming except you should choose names written as Yes or No questions
E.g. isSkyUp

4. Boolean Variables
What would you name each Boolean variable to represent the statements in the first table?
The sky is blue
The grass is pink
A snail is fast
The school is 3 stories high
A soccer ball is round and pink

5. Boolean Operators Like math has operators; +, -, x, ÷, etc.
Boolean logic has its own operators
AND (Turing command is and)
E.g. var isWeatherGood : boolean := isSkyBlue and isWarmOutside
OR (Turing command is or)
E.g. var willBallBounce : boolean := isBallRubber or isGroundRubber
NOT (Turing command is not)
E.g. var isDayTime : boolean := not(isNightTime)
Boolean logic is a fundamental concept in making decisions in programming

6. Boolean Operators AND: OR: NOT:
Evaluates to True when all elements are True,
Otherwise the result is False
OR:
Evaluates to True when at least 1 element is True,
NOT:
Evaluates to True when the entire expression is False,
NOTE: Whenever you use these operators you are creating a complex boolean expression called a Compound Expression

7. Truth Table Example (Follow BEDMAS)
Own Xbox (1)
Own PS3 (2)
1 AND 2
1 OR 2
NOT (1) AND NOT (2)
NOT (1 OR 2)
STEP 1: Fill out ALL possibilities for the basic information,
Columns 1 and 2 in this example
STEP 2: Fill out the rest of the table ONE COLUMN at a time
QUESTION: What do you notice from the last two columns
This shows us that NOT (A) AND NOT (B) = NOT (A OR B)

8. Question
Why do computer programs need to make decisions?
Interactivity – a program is like a movie if it does not change depending on the inputs, and it is not very useful if it is like a movie.

9. In Code
Below is an example of a simple program that determines if the user is both tired and hungry:
var isHungry : boolean
var isTired : boolean
var isUserTiredAndHungry : boolean
put “Are you tired (true or false)”
get isTired
put “Are you hungry (true or false)”
get isHungry
isUserTiredAndHungry := (isTired and isHungry)
put “The results of you being both tired and hungry are: “, isUserTiredAndHungry

10. Practice Time
Found on the Moodle under the “Selection” Section, compare your responses with another student.
Remember: When doing a truth table, fill out all of the possibilities for the base information first, then proceed column by column